1. Field of the Invention
The present invention relates generally to devices and methods for using impedance or resistance control to perform work within a pipe network, and, more specifically, the present invention is directed to robots capable of determining a local amount of impedance related to the performance of a predefined task and performing said task based upon the determined impedance.
2. Description of the Background
The oldest pipes in the United States date to the late 1800's, and the average non-rehabilitated water and sewer pipe is more than 50 years old. However, depending on the type of material used, pipe operating life ranges from only 50 to 125 years. Much of the existing pipe, therefore, needs to either be replaced or rehabilitated (relined or otherwise repaired) in short order.
A major problem in the U.S. sewer system is inflow and infiltration (“I&I”). I&I is caused by the inflow of rainwater into the sewer system due to heavy rains and/or the fact that many sewer lines lie below the water table. I&I increases costs at sewage treatment plants, and, in a number of cases, the additional water injected during a rainstorm outstrips the capacity of treatment plants. This often results in the diversion of raw sewage into rivers and streams.
Along the same lines, the biggest problem in the U.S. potable water system is leaky pipes. For example, estimates hold that 35% to 50% of drinking water in the U.S. is unaccounted for once it leaves a water treatment facility, the vast majority of which is lost through leaky pipes. The urgent need to rehabilitate water pipes exists to reduce water leakage from the system, reduce costly emergency break repairs and increase water quality at the consumer's tap.
Government regulation is also increasing in these areas. In June 1999, the GASB (Government Accounting Standards Board) issued “Statement 34” requiring state and local governments to report the value of their infrastructure assets such as buried pipes, storm sewers, bridges and roads. Additionally, the EPA is actively pursuing consent decrees—forcing cities to eliminate sewage overflow into rivers and other bodies of water during heavy rainfalls and to increase water quality nationwide. Finally, the Safe Drinking Water Act, first passed in 1974, requires municipal water suppliers to guarantee that the water quality at the tap is the same as the water quality at the purification plant. The decay, sediment and leakage taking place in either water pipes or water storage tanks accounts for impurities in drinking water that enter the system after the water leaves the water purification plant, and prevents the satisfaction of these government regulations.
In general, the three main functions required to maintain our piping infrastructure are: (1) cleaning; (2) inspecting; and (3) rehabilitating. Cleaning involves the removal of obstructions and debris that blocks the flow of water and sewage. Inspecting involves mapping the pipe interior, characterizing the pipe's defects, and developing a maintenance plan for the pipe. Rehabilitating the pipe involves maintaining and fixing faulty piping.
Many maintenance tasks are accomplished by deploying robots into pipes as part of methods to clean, inspect, or rehabilitate pipes, but these methods rely on manual operation to detect pipe locations, pipe edges, sediment and thickness of sediment, thickness of obstructions, cutting force necessary to cut through obstructions, or other aspects important for pipe maintenance. The present invention's impedance control methods, which automatically detect these various aspects by monitoring impedances encountered by robots, reduce the need for manual operator interaction and improve the speed, quality, and consistency of pipe maintenance tasks.
For example, contractors currently use dedicated trucks equipped with remote controlled cutters and video inspection equipment to perform cutting operations related to rehabilitation, including protruding tap cutting and lateral reinstatement among others. In these traditional methods, the operator directs the view of the camera and the forward motion of the remote cutter until the area of interest (typically the hole to be cut) is within the operator's sight (through the camera display). The operator then uses the view from the camera and a set of manually adjusted controls to direct the cutting bit in three axes of motion. By manually controlling the speed, depth, and direction (cutting path), he performs the cutting process.
During the process of cutting, the operator continuously views the image, stopping to adjust the controls to compensate for errors in the cutting bit speed and position. This approach is limited in speed, quality, and consistency because it relies on the skill and experience of the operator to perform the task.
One important limitation of efforts to use automatic robotic methods to, for example, cut open laterals after relining, stems from the fact that the lateral/main interface is not in a regular or predictable shape. Because laterals intersect with mains at a variety of different angles (and different size laterals), there is no way to “predefine” a cutting pattern to open the laterals after lining. The present invention, however, does not rely upon prior knowledge of the intersection, and is adaptable to all intersections.
Moreover, prior cutting methods rely upon recognition of the “dimple” or protrusion commonly caused in the new lining at the opening to a lateral in order to begin a lateral cutting operation (because cutting by sight is utilized). Since the only requirement for the impedance method of the present invention is to get the tool to plunge inside the lateral opening, in pipes where there are no dimples (or in pipes that are filled with an opaque fluid which does not allow visual perception, the present methods can still be employed with accurate odometry and clocking information on the location of the lateral openings from a pre-lining inspection.
In much the same way, prior methods relied upon a high degree of accuracy in determining the pre-cutting pose of the robot (and matching the robot's actual pose to a pre-programmed intended pose). The present invention has no such limitation.
Finally, traditional robots cannot autonomously perform work within a pipe because they cannot correctly adjust the cutting path in the same manner a manual operator would make adjustments in response to visual cues. Because current cutting robots do not even attempt to adjust to changing conditions, such as different lining materials or dulled cutting bits encountered from cut-to-cut, they must rely on a manual operator for proper cutting. The impedance control methods of the present invention allow robots to automatically adjust to changing conditions in different situations by measuring impedance characteristics for each unique circumstance.
A wide variety of traditional methods for removing sediment or sealing pipe joints (or other manual processes) can be partially or fully automated with the impedance methods of the present invention. These and other new robotic devices and methods are continually sought to address these and other limitations of the prior art. Specifically, robotic devices that can monitor impedances and autonomously detect aspects important for pipe maintenance based on changes in these impedances in various circumstances without the need for extensive (or any) operator interaction are greatly desired. The present invention, in its many preferred embodiments, addresses these and other limitations of the prior art.